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Spatial sound reproduction

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20120328109 patent thumbnailZoom

Spatial sound reproduction


An apparatus for spatial sound reproduction comprises a receiver (101) for receiving a multi-channel audio signal. An analyzer (107) determines a spatial property of the multi-channel audio signal, such as a spatial complexity or organization. A selection processor (109) then selects a reproduction mode from a plurality of sound reproduction modes where the multi-channel sound reproduction modes employ different spatial rendering techniques. A reproduction circuit (103) then drives a set of loud-speakers (105) to reproduce the multi-channel audio signal using the selected reproduction mode. The switching between the reproduction modes may be fast (e.g. in the order of 100 ms to 10 secs) thereby allowing a short term adaptation of the reproduction mode to the signal characteristics. The approach may in particular provide an improved spatial experience to a listener.

Browse recent Koninklijke Philips Electronics N.v. patents - Eindhoven, NL
Inventors: Aki Sakari Harma, Werner Paulus Josephus De Bruijn
USPTO Applicaton #: #20120328109 - Class: 381 17 (USPTO) - 12/27/12 - Class 381 
Electrical Audio Signal Processing Systems And Devices > Binaural And Stereophonic >Pseudo Stereophonic

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The Patent Description & Claims data below is from USPTO Patent Application 20120328109, Spatial sound reproduction.

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FIELD OF THE INVENTION

The invention relates to spatial sound reproduction and in particular, but not exclusively, to spatial sound reproduction including upmixing of a multi-channel audio signal.

BACKGROUND OF THE INVENTION

Spatial sound reproduction in the form of stereo recordings and reproduction has been around for several decades. In the last decades, more advanced arrangements and signal processing have been used to provide improved spatial listening experiences. In particular, the use of surround sound using e.g. 5 or 7 spatial speakers has become prevalent to provide an enhanced experience in connection with e.g. viewing of movies or television. In addition, compact multi-driver loudspeaker systems such as ‘sound bars’ have become popular option for the traditional stereo and 5.1 systems. Those devices provide an experience of a wide spatial audio image for a listener even from a small device. This is based on digital processing of the signals and special physical arrangement of the device.

Spatial sound processing increasingly utilizes advanced signal processing as part of the sound reproduction to provide an improved spatial experience. For example, complex algorithms may be used to upmix an audio signal to a higher number of channels. For example, a 5 channel surround signal may at the transmitting side be downmixed to a stereo or mono signal. This signal is then distributed and the sound reproduction includes an upmixing of the received signal to the original 5-channel signal.

As another example, signal processing may be used to provide a sound widening effect to a stereo signal resulting in the listener experiencing a wider sound stage. Typically the methods are based on signal processing operations that reduce the correlation between the channels. These techniques are particularly popular in the compact loudspeaker systems mentioned above.

As another example, reproduction of a spatial signal may include an extraction of a dominating sound source in e.g. a stereo signal. The remaining residual signal will typically correspond to the ambient stereo image which is more diffuse. The dominant signal and the ambient signal may then be reproduced differently such that the reproduction characteristics are optimized for each signal.

However, although such spatial sound reproduction techniques improve the listening experiences, there tends to be some associated disadvantages. In particular, the reproduction may not provide an optimal spatial experience in all situations and the signal processing may in some cases actually result in a degraded spatial experience.

Hence, an improved system for spatial sound reproduction would be advantageous and in particular a system allowing for increased flexibility, facilitated operation, facilitated implementation, an improved spatial listening experience and/or improved performance would be advantageous.

SUMMARY

OF THE INVENTION

Accordingly, the Invention seeks to preferably mitigate, alleviate or eliminate one or more of the above mentioned disadvantages singly or in any combination.

According to an aspect of the invention there is provided an apparatus for spatial sound reproduction, the apparatus comprising: a receiver for receiving a multi-channel audio signal; a circuit for determining a spatial property of the multi-channel audio signal; a circuit for selecting a selected reproduction mode from a plurality of sound reproduction modes, the multi-channel sound reproduction modes employing different spatial rendering techniques; and a reproduction circuit for driving a set of spatial channels provided by a set of loudspeakers to reproduce the multi-channel audio signal using the selected reproduction mode.

The invention may provide improved sound reproduction in many embodiments. In particular, an improved spatial experience may be provided in many scenarios. Typically, the spatial reproduction may be improved for the specific audio signal. The Approach may further allow a low complexity implementation and facilitated operation in many embodiments.

The selection of an appropriate reproduction method may be optimized for the specific conditions experienced while maintaining low complexity.

The spatial property may be indicative of a spatial organization and/or a spatial complexity of the signal. For example, the spatial property may be indicative of the presence of one or more dominant sound sources in accordance with a suitable criterion or process for extracting dominant sound sources. In some embodiments, the spatial property may be indicative of a spatial distribution of sounds sources in the sound image represented by the multi-channel signal.

The set of loudspeakers may specifically be loudspeakers of a surround sound setup comprising e.g. 3, 5 or 7 spatial speakers (in addition to possibly a non-spatial Low Frequency Effect speaker or subwoofer). The set of loudspeakers may be multi-driver loudspeaker systems with typically three or more individually driven loudspeakers (or loudspeaker arrays) in one physical device. The set of loudspeakers may also comprise a plurality of such devices.

In accordance with an optional feature of the invention, at least one of the sound reproduction modes comprises at least one of: an upmixing to higher number of spatial channels than a number of channels of the multi-channel audio signal; and a down-mixing to a lower number of spatial channels than the number of channels of the multi-channel audio signal.

The invention may provide an improved spatial experience. For example, some sound images of a stereo signal may provide an improved spatial experience when reproduced as a mono-signal. Other sound images of a stereo signal may provide an improved spatial experience when reproduced as a widened stereo signal combined with a center-signal, i.e. when reproduced using three spatial channels.

In accordance with an optional feature of the invention, the set of spatial channels comprise a different number of channels than the multi-channel audio signal.

The invention may provide an improved spatial experience for a sound reproduction system and may in particular allow additional degrees of freedom in adapting the sound reproduction to the specific sound image and spatial characteristics.

In accordance with an optional feature of the invention, a maximum switch frequency for switching between sound reproduction modes exceeds 1 Hz.

This may provide a dynamic adaptation and optimization which may closely match the varying characteristics of the audio thereby providing an improved listening experience.

The feature may allow improved performance and improved adaptation of the reproduction mode to the audio signal thereby providing an enhanced listening experience.

The approach may allow a short term adaptation of the reproduction to the signal characteristics.

In some embodiments, a maximum switch frequency for switching between reproduction modes may exceed 0.01 Hz; 0.1 Hz, or even 10 Hz.

The maximum switch frequency may be the maximum frequency at which the apparatus can switch between reproduction modes. The maximum frequency may be restricted by the design parameters of the system including characteristics of the spatial property estimation and switching functionality.

In accordance with an optional feature of the invention, the circuit for determining the spatial property is arranged to determine the spatial property with a time constant of no more than 10 seconds.

This may provide a dynamic adaptation and optimization which may closely match the varying characteristics of the audio thereby providing an improved listening experience.

The feature may allow improved performance and improved adaptation of the reproduction mode to the audio signal thereby providing an enhanced listening experience. The approach may allow a short term adaptation of the reproduction to the signal characteristics.

In some embodiments, the circuit for determining the spatial property may advantageously be arranged to determine the spatial property with a time constant of less than 500 seconds, 100 seconds, 1 second, 500 ms, 100 ms or even 50 ms.

The time constant represents the time it takes the spatial property to reach 1-1/e·63% of its final (asymptotic) value following a step change.

In some embodiments, the circuit for determining the spatial property is arranged to include a low pass filtering of the spatial property, the low pass filtering having a 3 dB cut-off frequency exceeding 0.001 Hz, 0.01 Hz, 0,1 Hz, 1 Hz, 10 Hz or 50 Hz.

In accordance with an optional feature of the invention, the plurality of sound reproduction modes comprises at least one of: a monophonic reproduction mode; a reproduction mode maintaining spatial characteristics of the multi-channel signal; a reproduction mode comprising spatial widening processing; and a reproduction mode comprising a separation into at least one dominant source signal and an ambiance signal, and applying different spatial reproduction of the at least one primary source signal and the ambiance signal.

These reproduction techniques may be particular advantageous and suited to provide improved listening characteristics for different audio characteristics. In many embodiments, the plurality of sound reproduction modes may advantageously comprise two, three or all four reproduction modes as these are particularly suited to different characteristics, and thus together provide a set of modes that provide improved reproduction for a large range of audio characteristics. The techniques may specifically together provide suitable reproduction characteristics for a wide range of audio signals.

In accordance with an optional feature of the invention, the apparatus further comprises: a circuit for determining a content characteristic for the multi-channel audio signal; and wherein the circuit for selecting is arranged to further select the selected reproduction algorithm in response to the content characteristic.

This may further improve the adaptation of the reproduction and provide an improved spatial experience in many embodiments. The content characteristic may for example be determined by a content analysis of the multi-channel audio signal and/or an associated video signal.

In accordance with an optional feature of the invention, the circuit for determining the content characteristic is arranged to determine the content characteristic in response to meta-data associated with the multi-channel audio signal.

This may provide a particularly accurate and low complexity approach that may be advantageous in many embodiments.

In accordance with an optional feature of the invention, the circuit for reproducing the multi-channel audio signal is arranged to adapt a characteristic of a spatial rendering technique of the selected reproduction mode in response to the content characteristic.

This may further improve the adaptation of the reproduction and provide an improved spatial experience in many embodiments.

In accordance with an optional feature of the invention, the circuit for reproducing the multi-channel audio signal is arranged to adapt a characteristic of a spatial rendering technique of the selected reproduction mode in response to the spatial property.

This may further improve the adaptation of the reproduction and provide an improved spatial experience in many embodiments.

In accordance with an optional feature of the invention, the spatial processing characteristic is a degree of spatial widening applied to at least two channels of the multi-channel audio signal.

This may provide a particularly advantageous optimization as the spatial widening may provide a significantly enhanced spatial experience for some audio characteristics but may degrade the spatial experience for other audio characteristics. Accordingly, an optimization of the spatial widening to the audio characteristics may provide a particularly advantageous performance.

In accordance with an optional feature of the invention, the circuit for reproducing the multi-channel audio signal is arranged to gradually transition from a first selected reproduction algorithm to a second selected reproduction algorithm.

This may provide improved performance and may in particular reduce the noticeability of changing between different reproduction modes. The apparatus may specifically be arranged to, during a transition interval, generate drive signals for the set of loudspeakers using both the first selected reproduction algorithm and the second selected reproduction algorithm and to drive the set of loudspeakers by signals generated as a weighted combination of the drive signals where the weighting is dynamically changed during the transition interval.

In accordance with an optional feature of the invention, the circuit for determining the spatial property is arranged to determine the spatial property in response to an energy indication for a combined signal of at least two channels of the multi-channel audio signal relative to an energy indication for a difference signal of the at least two channels.

This may be a particularly advantageous spatial property for adapting the spatial reproduction. In particular, it may provide an advantageous trade-off between accuracy and complexity for many scenarios.

In accordance with an optional feature of the invention, the circuit for determining the spatial property is arranged to decompose the multi-channel audio signal into at least one dominant sound source signal and a residual signal, and to determine the spatial property in response to an energy indication for the dominant sound source signal relative to an energy indication for the residual signal.

This may be a particularly advantageous spatial property for adapting the spatial reproduction. In particular, it may provide an advantageous trade-off between accuracy and complexity for many scenarios.

According to an aspect of the invention there is provided a method of spatial sound reproduction, the method comprising: receiving a multi-channel audio signal; determining a spatial property of the multi-channel audio signal; selecting a selected reproduction mode from a plurality of sound reproduction modes, the multi-channel sound reproduction modes employing different spatial rendering techniques; and driving a set of loudspeakers to reproduce the multi-channel audio signal using the selected reproduction mode.

These and other aspects, features and advantages of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will be described, by way of example only, with reference to the drawings, in which

FIG. 1 is an illustration of an example of a system for spatial sound reproduction in accordance with some embodiments of the invention;



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stats Patent Info
Application #
US 20120328109 A1
Publish Date
12/27/2012
Document #
13521069
File Date
01/26/2011
USPTO Class
381 17
Other USPTO Classes
International Class
04R5/00
Drawings
4



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